it is because racist is a powerful word that really has no equal when hurled at whites if they can keep racist exclusive to whites then they hold power over them discriminatory on the other hand is far less powerful a word so they are willing to accept that accusation but still have the upper hand they can say yes i discriminate but look at whitey over there hes a racist the exact same game is used over rapist which is kept exclusive for men because the sexual assault that women are legally capable of doing sounds much less severe than rape it is a clever game but i think we are starting to see the turn against it as people realise how bullshit it it tldr racist to a white nigger to a black